Tensile test Report: Khurshidanjum Pathan, group (A1a)
Abstract: The purpose of tensile test is to calculate tensile strength; percentage elongation and percentage reduction of area after fracture through data analysis for Mild Steel, Copper and Aluminium Aluminium by applying maximum load until it break. As a result it is possible to choose between the three different materials by the analysis and comparison of uncertainties, yield and tensile strength, ductility and stiffness. In this test sample of material to be tested is being set in tensile test machine and load being applied until it fractured and in between all the data were being recorded.
Introduction In this experiment specimen rod of Mild steel with diameter of 10.06 mm, copper rod with diameter of 9.94 mm, and Aluminium Alloy with diameter of 10.07 mm were tested until it fractured. In this tensile test the relevant material properties can be obtain and from the results how different materials behave under similar load can be determined. Tensile Test Machine
Clip on extensometer
Objectives •
•
•
•
•
•
To understand how different materials behave under uniaxial tension load. To determine the basic stress-strain response for different materials. Determine and compare the mechanical and material properties of various materials. Plot Stress versus Strain for steel for linear region, part of yield region, and for whole range of extension. Calculate tensile strength, % elongation and % reduction of area after fracture for mild steel, copper and aluminium alloy. And young’s modulus, yield stress and 0.1% proof stress for mild steel. Determine the measurement errors and uncertainties.
Theory: The maximum load is the greatest load that the specimen can withstand without breaking. (12) The breaking load is the load at which the specimen breaks. (12)
The Yield Point is the first point at which permanent deformation of stressed specimen begins to take place. This is a point on the stress-strain curve at which the increase in strain is no longer proportional to the increase in stress. (13) 0.1% or 0.2% proof stress: When yield point is not easily defined based on stress-strain curve an offset yield point is arbitrary defined. The value for this is commonly set at 0.1 or 0.2% of the strain. High strength steel an aluminium alloy do not exhibit a yield point so this off set yield point is used on these kind of materials. (14) The percentage Elongation is a measurement of the deformation at the point of final fracture. % elongation is extent the specimen stretches before it fractures (12)
Where LO = Original gauge length, LU = Final length after fracture
The percentage reduction in area after fracture is measured by fracture ductility. This range from zero for brittle materials to high values (100%) for ductile material.
Where SO= Original cross section area, SU= Final area after fracture
Engineering Strain:
ε
=
l i − l o l o
=
∆l
l o
Where, Ԑ is the engineering strain l o is initial gauge length, and li is the instantaneous gauge length. (15) Engineering Stress:
(15)
Yield Stress is defined as a stress at which a predetermined amount of permanent deformation occurs (16). Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed (14) Upper Yield Stress is value of stress at the moment when first decrease in force is observed. Lower Yield Stress is taken to be yield strength when yield point elongation is observed this is the lowest value of stress at yield point. Breaking Strength is a stress required to break the material. It is measured in Newton per square millimetres of area. Tensile (yield) strength is very important value for engineering structure design. The maximum tensile load sustained by a specimen during a tension test, divided by the original cross-sectional area. The maximum engineering stress sustained. Results are expressed in Newton per square millimetres of area. (17)
Young’s Modulus is measures of stiffness of an elastic material and is a quantity used to characterize material. It is defined as the ratio of the uniaxial stress over the uniaxial strain. It is expressed in Pascal (Kilo, Mega, and Giga). (18)
Method & Approach:
Firstly, for all of the three materials the original gauge lengths (mean diameter) were measured by taking an average with help of micrometer and we worked out the cross section area for each of the material. Lindley extensometer was being fixed to steel specimen. Then this specimen then inserted into the upper jaw of the testing machine with extensometer. It’s necessary to adjust the load scale to zero at every time you record load. Engage the lower jaws of the testing machine with steel specimen. Check the functionality of the extensometer by applying a small load (1 or 2 kN). When the necking begun the extensometer was removed and the elongation of the specimen was recorder using a ruler. The load applied methodically and unhurriedly until the steel specimen fractured. The same process was applied for Copper and Aluminium Alloy specimen.
Result: Tensile strength, Breaking strength, Percentage elongation and Percentage reduction of area after fracture were tabulated from the results for Mild steel, Copper and Aluminium alloy. For Mild Steel specimen full reading were taken until it fractured see Table (1) Stress - strain graph for steel were plotted for linear region only Figure (1)
The young’s modulus was calculated with help of Figure (2) which was calculated to 211 GPa for steel. Stress – Strain graph for steel for linear region and yield region were plotted see figure (2). From the same graph Yield stress of 374 MPa and 0.1% proof stress of 308 MPa were located. Figure (3) show the Stress- Strain graph for steel for the whole range of the extension. Table: 2
Breaking Load (lbs) Minimum Diameter at Fracture τ (inch) Maximum Load (lbs) Fractured Area (mm^2) Elongation (mm) Final length (LU) (mm) Final Cross Sectional Area (SU) (mm^2) Fractured Diameter (mm) Diameter (mm) Gauge Length (LO)(mm) Original Area (SO) (mm^2)
Mild Steel 5280
Copper 3200
Aluminium Alloy 11200
0.219 8360 24.30 13 37
0.198 4880 19.86 16 34
0.351 12080 62.43 5 45
55.18 5.56
57.74 5.03
17.22 8.92
10.06 50 79.49
9.94 50 77.60
10.07 50 79.64
1 Lb (g) g (N) 1 inch (mm)
453.6 9.81 25.4
Table: 3 Tensile Strength (MPa) Yield Stress (MPa) 0.1% of Proof Stress (MPa) Young's Modulus (GPa) % Elongation (LO-LU)/LO *100 (mm) % reduction In Area (SOSU)/SO*100 (mm^2) Breaking strength (MPa)
Mild Steel 468 374 308 211
Copper 280 n/a n/a n/a
Aluminium 675 n/a n/a n/a
26
32
10
31 296
26 183
78 626
Breaking strength =
Tensile Strength =
Young’s modulus =
% Elongation
mm
Where LO = Original Length, LU = Final length
% reduction of area = Where SO = Original cross sectional area, SU = Final cross sectional area
Uncertainties: Tensile strength
=
Uncertainties in Tensile Strength =
=
Mild Steel,
=
=1.196
Pascal
=1.589
Pascal
Copper,
=
Aluminium Alloy,
=
=6.5923
Mild Steel,
=
= 0.31
Copper,
=
= 0.26
Aluminium Alloy,
=
= 0.78
Mild Steel:
Pascal
=
= (1.196
Pascal) + (0.31
=
= (1.589
Pascal) + (0.26
=
Pascal) + (0.78
=
0.310 N/
Copper:
= 0.260 N/
Aluminium Alloy:
= 0.78 N/
Graphs
= (6.59
Figure (1)
Figure (2)
Figure (3)
Discussion In figure (1) graph the linear region of steel is elastic and where elasticity ends plasticity begins at a yield point. After a yield point the slope is steep which means Young’s modulus is high for the steel. Steel starts to plastically deform after this point until it break. Just after the ultimate tensile strength point steel is being fractured.
Comparison of tensile strength states that Aluminium Alloy has the highest tensile strength which means its strong material and cannot be easily plastically deform and require large amount of force to deform. While Mild steel has 2 nd highest tensile strength and copper has lowest which means copper is soft material compared to aluminium and steel, can easily deform. In contrast steel and copper both are ductile material therefore tensile strength is relatively unimportant as too much plastic deformation takes place. Breaking Strength states how strong is material to break. Aluminium has high breaking strength while steel and copper has relatively low breaking strength which means aluminium is hard material to break in comparison of steel and copper. Percentage reduction in area show the how much area of material became thin after fracture. In which Aluminium has lowest area where thinning has undergone while copper has relatively large area. The percentage elongation states the plastic deformation before material breaks. This is used to check the ductility of a material. Mile steel and Copper are ductile material as they have relatively large % of reduction area and elongation then Aluminium therefore, when these materials are in tension it result in large plastic deformation before they fracture. While Aluminium is the other way round it is not a ductile material so it is rare for plastic deformation to take place before the fracture. Copper is weak material as it has low tensile strength and therefore it can be easily deform before fracture and it is easy to shape this material also it has high thermal and electrical conductivity therefore, used in machinery industry Steel is stiff and ductile material which can withstand large amount of force therefore it is being used in car industry and rail industry as it can easily deform before the fracture.
Aluminium Alloy has high tensile strength and breaking strength so it’s very hard material which cannot be break easily therefore, it is used in air industry as this material require grater force to break.
Conclusion The experiment has satisfactory result as Young’s modulus has acceptable value of 211 GPa which is near to range value of 200 GPa. However, there is a difference which could be result of measurement errors, human error, accuracy error, random error and precision error. Steel material being used for the test was old and rusty so there is a possibility of difference in cross section area or specimen could have contained impurities. Steel and copper are ductile material so plastic deformation takes place before fracture. Aluminium Alloy is strongest material with high tensile and breaking strength. This test is performed for the first time so there is possibility of errors in calculation which can definitely improved in second or third attempt. The calculated material property is used to select material for any specific industry. Errors cannot be avoid however, it can be minimized, if the measurement was taken carefully
Appendices
Table 1: Load (lbs) 0 1720 2200
Load (kN) 0.00 7653.68 9789.60
Extension (mm) 0 0.005 0.01
Stress (Mpa) 0 96 123
Strain(mm) 0 0.0001 0.0002
2620 3100 3520 4060 4260 4780 5180 5500 6000 6200 6580 6680 6420 6400 6400 6500 6520 6540 6540 6540 6580 6580 6480 6560 6580 6580 6580 7380 7700 8000 8160 8260 8320 8360
11658.52 13794.43 15663.35 18066.25 18956.22 21270.12 23050.05 24473.99 26698.90 27588.86 29279.79 29724.77 28567.82 28478.82 28478.82 28923.80 29012.80 29101.80 29101.80 29101.80 29279.79 29279.79 28834.81 29190.79 29279.79 29279.79 29279.79 32839.64 34263.58 35598.53 36310.50 36755.48 37022.47 37200.46
0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05 0.055 0.06 0.065 0.07 0.075 0.08 0.085 0.09 0.095 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 2 3 4 5 6 7 8
147 174 197 227 238 268 290 308 336 347 368 374 359 358 358 364 365 366 366 366 368 368 363 367 368 368 368 413 431 448 457 462 466 468
0.0003 0.0004 0.0005 0.0006 0.0007 0.0008 0.0009 0.001 0.0011 0.0012 0.0013 0.0014 0.0015 0.0016 0.0017 0.0018 0.0019 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16
The data and calculations for mild steel, Copper and Aluminium alloy
Mild Steel:
Average diameter (mm) = (10.11+ 10.07 + 10.01) / 3 = 10.06 mm Original cross sectional area (mm2) = 79.49 mm2
π
d2/4 =
π
(10.06)2/4 =
Diameter after fracture (mm) = 5.56 Cross sectional area after fracture (mm2) = = 24.30 mm2
π
d2/4 =
π
(5.56)2/4
Maximum load = (8360lbs*453.6*9.81) = 37.2mN Breaking load = (5280 lbs * 453.6*9.81) = 23.5 mN % Reduction in area = ((79.45 – 24.28)/ 79.45) X 100 = 69.4 % % Elongation = ((50-37) / 50) X 100 = 26% Tensile strength = (37.2 mN)/ (79.49*10^3) = 468 MPa Breaking strength = (23.5mN) / (79.49*10^3) = 296 MPa
Copper:
Average diameter (mm) = (9.93+9.93+9.95) / 3 = 9.94 mm Original cross sectional area (mm2) = 77.60 mm2
π
d2/4 =
π
(9.94) 2/4 =
Diameter after fracture (mm) = 5.03 Cross sectional area after fracture (mm2) = = 19.87 mm2
π
d2/4 =
π
(5.03)2/4
Maximum load = (4880lbs*453.6*9.81) = 21.7mN Breaking load = (3200 lbs * 453.6*9.81) = 14.2 mN % Reduction in area = ((77.60 – 19.87)/ 77.60) X 100 = 74.4 % % Elongation = ((50-34) / 50) X 100 = 32% Tensile strength = (21.7 mN)/ (77.60*10^3) = 280 MPa Breaking strength = (14.2mN) / (77.60*10^3) = 183 MPa
Aluminium Alloy:
Average diameter (mm) = (10/06+10.07+10.07) / 3 = 10.07 mm Original cross sectional area (mm2) = 79.64 mm2
π
d2/4 =
π
(10.07)2/4 =
Diameter after fracture (mm) = 8.92 Cross sectional area after fracture (mm2) = = 62.49 mm2
π
d2/4 =
π
(8.9)2/4
Maximum load = (12080lbs*453.6*9.81) = 53.8 mN Breaking load = (11200 lbs * 453.6*9.81) = 49.8 mN % Reduction in area = ((79.64 – 62.49)/ 79.6) X 100 = 21.6 % % Elongation = ((50-45) / 50) X 100 = 10% Tensile strength = (53.8 mN)/ (79.64*10^3) = 675MPa
Breaking strength = (49.8mN) / (79.64*10^3) = 626 MPa
Bibliography
(12) http://www.coursework.info/University/Engineering/Tensile_test_report_L88541.html (13) http://composite.about.com/library/glossary/y/bldef-y6168.htm (14) http://en.wikipedia.org/wiki/yield_(engineering) (15) William F. Smith: Foundations of Materials Science and Engineering, second edition, McGraw-Hill, 1993.
(16) http://engineersedge.com/material_science/yield_strength.htm (17) http://composite.about.com/library/glossary/t/bldef-t5443.htm (18) http://en.wikipedia.org/wiki/youngs_modulus
